Neurodegenerative diseases are generally characterized by a degeneration of neurons in either the brain or the nervous system of an individual. Amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), and multiple sclerosis (MS) fall within this category. These diseases are debilitating, the damage that they cause is often irreversible, and the outcome in a number of cases is fatal.
ALS is characterized by gradual degeneration of motor neuron cells in the spinal cord and brain, which ultimately leads to progressive weakness and paralysis of muscle and death. ALS occurs in two clinically indistinguishable forms, referred to as a sporadic form and a familial form. The pathogenesis of ALS is incompletely understood, although different hypotheses have been suggested, including mitochondria dysfunction, mutation in the superoxide dismutase gene, and defects in neuronal glutamate transport. Autoimmunity has also been hypothesized to be involved in ALS pathogenesis (Appel et al. 1993. J. Neurol. Sci. 118:169-174). In addition, several recent studies have suggested that the immune system may be actively involved in the disease process of ALS, with observations of activated microglia, IgG deposits, increased FcR expression, and dysregulation of cytokine expression in the spinal cord of ALS patients (Troost et al. 1989. Clin. Neuropathol. 8:289-294; Engelthardt et al. 1990. Arch. Neurol. 47:1210-1216; Schiffer et al. 1996. J. Neurol. Sci. 139(suppl):27-33; Hayashi et al. 2001 J. Neurol. Sci. 188:3-7.9-12).
Recent clinical and pathological studies have shown that involvement outside the motor neuron system is relatively common in Amyotrophic Lateral Sclerosis (ALS) (Hayashi et al. 2001, supra; Obal et al. 2001 Neuroreport. 12:2449-2452; Sola et al. 2002 8. Eur. Neurol. 47:108-112; Ono et al. 2001 J. Neurol. Sci. 187:27-34; Alexianu et al. 2001 Neurology. 57:1282-1289.). Microglia/macrophage activation and inflammatory response have been implicated in ALS disease progression (Appel et al. 1993, supra; Engelthardt et al. 1990, supra; Hayashi et al. 2001 supra; Obal et al. 2001 Neuroreport. 12:2449-2452; McGeer et al. 2002 Muscle Nerve. 26:459-47028, 29). However, few studies to date have explored the status of the systemic immune response in ALS. Despite intensive investigation, ALS has no known cause or effective therapy.
Retroviral infection has recently been implicated in the pathogenesis of an ALS-like syndrome in patients with HIV-associated disease. Moulignier et al. (Reversible ALS-like disorder in HIV infection. Neurology. 57:995-1001) recently reported the outcome of six HIV-1-infected patients with a neurologic disorder mimicking ALS and all those patients stabilized or improved with antiretroviral therapy. MacGrowen et al. (2001. An ALS-like syndrome with new HIV infection and complete response to antiretroviral therapy. Neurology. 57:1094-10) also reported a dramatic clinical response to antiretroviral therapy in an ALS-like syndrome with new HIV infection.
Approximately one-quarter of individuals with AIDS develop neuropathological symptoms. Infection by HIV-1 causes inflammation within the brain and neuronal degeneration (Power et al. 2001 Adv. Virus. Res. 56:389-433), resulting in HIV-associated dementia (HAD) or the less severe minor cognitive and motor disorders (Janssen et al. 1991 Report of a Working Group of the American Academy of Neurology AIDS Task Force. Neurology. 41:778-785; McArthur et al. 1993 Multicenter AIDS Cohort Study. Neurology. 43:2245-2252; The Dana Consortium. 1996. Clinical confirmation of the American Academy of Neurology algorithm for HIV-1-associated cognitive/motor disorder. The Dana Consortium on Therapy for HIV Dementia and Related Cognitive Disorders. Neurology. 47:1247-1253.).
The mechanisms underlying HIV-associated neuronal injury are incompletely understood. Various studies have suggested that monocytes/macrophage activation may play a significant role in the pathogenesis of many neurological diseases (Smits et al. 2000 Eur. J. Clin. Invest. 30:526-535; Fiala et al. 2002 Eur. J. Clin. Invest. 32:360-371; Minagar et al. 2002 The role of macrophage/microglia and astrocytes in the pathogenesis of three neurologic disorders: HIV-associated dementia, Alzheimer disease, and multiple sclerosis. J. Neurol. Sci. 202:13-23), including HIV-associated neurologic disorders (Pulliam et al. 1997 Lancet. 349:692-695; Diesing et al. 2002 AIDS Reader. 12:358-368). Indeed, the best pathological correlate for HIV-associated neurologic disorders, especially HAD, is the number of activated mononuclear phagocytes (perivascular and parenchymal blood-derived macrophages and microglia), not the absolute levels of virus in brain per se (Glass et al. 1995 Ann. Neurol. 38:755-762; Adamson et al. 1999 Mol. Med. 5:98-109). Similar findings have been reported for simian AIDS related encephalopathy (SIVE) (Williams et al. 2002 Am. J. Pathol. 161:575-585). Macrophage activation has been reported in spinal cords of patients with ALS disease (Appel et al. 1993, supra; Engelthardt et al. 1990, supra; Obal et al. 2001, supra; McGeer et al. 2002, supra), although the role of macrophage activation in ALS pathogenesis has not been previously determined.
Studies on blood from patients with HAD (Liu et al. 2000 J. Neurovirol. 6(suppl 1): S70-81) and monkeys with SIVE (Williams et al. 2002 Am. J. Pathol. 161:575-585) have shown a direct relationship between the presence of activated blood macrophages and central nervous system (CNS) disease. These activated macrophages are thought to mediate blood brain harrier (BBB) breakdown and directly contribute to CNS pathogenesis.
Alzheimer's disease (AD) is the most common form of dementia among the elderly. Various studies have suggested that macrophage activation may be involved in AD (see, e.g., WO 99/21542). Currently the only definite way to diagnose AD is by post-mortem autopsy to assess the presence of amyloid plaques and tangles in brain tissue. Thus, AD diagnosis is generally a diagnosis of “possible” or “probable” AD. At specialized centers, doctors can diagnose AD correctly up to 90 percent of the time. Several tools are used to diagnose “probable” AD, including medical history, analysis of blood urine, or spinal fluid, to rule out other causes (e.g., thyroid deficiencies, infectious disease, etc.), brain scans, and neuropsychological tests to asses memory, problem solving, attention, counting, and language.
Multiple sclerosis (MS) is a chronic disease that is characterized by “attacks,” during which areas of white matter of the central nervous system, known as plaques, become inflamed. Inflammation of these areas of plaque is followed by destruction of myelin, the fatty substance that forms a sheath or covering that insulates nerve cell fibers in the brain and spinal cord. Myelin facilitates the smooth, high-speed transmission of electrochemical messages between the brain, spinal cord, and the rest of the body. Damage to the myelin sheath can slow or completely block the transmission of these electrochemical messages, which can result in diminished or lost bodily function.
The most common course of MS manifests itself as a series of attacks, which are followed by either complete or partial remission, during which the symptoms lessen only to return at some later point in time. This type of MS is commonly referred to as “relapsing-remitting MS.” Another form of MS, called “primary-progressive MS,” is characterized by a gradual decline into the disease state, with no distinct remissions and only temporary plateaus or minor relief from the symptoms. A third form of MS, known as “secondary-progressive MS,” starts as a relapsing-remitting course, but later deteriorates into a primary-progressive course of MS.
The symptoms of MS can be mild or severe, acute or of a long duration, and may appear in various combinations. These symptoms can include vision problems such as blurred or double vision, red-green color distortion, or even blindness in one eye, muscle weakness in the extremities, coordination and balance problems, muscle spasticity, muscle fatigue, paresthesias, fleeting abnormal sensory feelings such as numbness, prickling, or “pins and needles” sensations, and in the worst cases, partial or complete paralysis. About half of the people suffering from MS also experience cognitive impairments, such as for example, poor concentration, attention, memory and/or judgment. These cognitive symptoms occur when lesions develop in those areas of the brain that are responsible for information processing.
Despite the progress in the field, there remains a need for a therapy for treatment of ALS and MS, including alleviation of symptoms of these diseases. The present invention addresses this need.